Help CIS gurus

[Peter Voullaire]

Hello.
I am new to this board.
I have a 1980 911SC. It is K-Jet with Lambda.
This explaination of the problem is long so please bear with me.
I have read the Probst Bosche FI book.
The problem is that the car leans out and runs out of power above 3500 rpm in any gear, but is most noticable in the higher gears. Bascally the car run exactly as it should up to half throttle, but if you put your foot down any more the engine leans out. As you ease your foot back off the gas the car comes back to life.
The things I have replaced and checked follow... New fuel pump, new O2 sensor, new fuel filter, new lambda relay. The engine compressions are good. The tappets are set. The timing advances to 26 degrees. The fuel pressure is in spec, as is the fuel flow. The Control pressure hot and cold is in spec, as is the control pressure fuel flow. The Computer is fine, the frequency valve works, and the duty cycle is in the usual range.
The fuel injectors have been checked for spray pattern and volume, and are fine.
The car starts well hot and cold and runs just like it should. (up to half throttle)
The idle screw however has to be fully closed to get the idle to stay at 1000 rpm. The engine does not stumble when I take the oil filler cap off, so I have an air leak there but I cannot understand how this could cause the leaning off I suffer. I can legally bypass all the emissions devices on this car here in New Zealand. I will do this soon as see what happens.
The sensor plate moves freely, and when pushed up with the fuel pump running, heaps of gas comes out, but when the engine is back together and under load it just is not performing.
I have had the car on a Dyno, and the machanic shut the engine down straight away when he saw it lean out. It is definitely a fuel problem. It was making a massive 90hp at the rear wheels. No it is not a 912 engine in it!
Is there anything that I have missed?
Has anyone experienced this sort of problem?

Any suggestions appreciated.
Thanks
Peter Voullaire

[robs]

Peter, how did you verify fuel pressure and fuel flow?
Did you run the engine with the O2 sensor unplugged (for a fixed duty cycle) ?
Did you check the fuel accumulator ?
Since the engine does not stumble with the oil filler cap off, check if the oil trap (parts 47A,47B) between the intake rubber boot (part 18) and the hose from the oil tank is plugged:
http://www.pelicanparts.com/911/911_Parts/1978-83/1-7-2.JPG
Maybe you can check how much the airflow sensor plate lifts under load.
Just an idea - knot a thin twine to the lever of the plate and tape it to the inside of the air box, so that the twine is pulled easily through the piece of tape when the sensor plate lifts up.
If you suspect an air leak you cannot find, take out the whole CIS in one piece: remove the 12 nuts from the intake runners and 1 nut at the throttle level plate (part 64).
Good luck


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Robert / 80 Targa

[IDrabble]

I had the exact same problem. It turned out to be the fuel pick up pipe between the tank and the pump.Everything was OK when stationary but when driving under load the pipe was sucking in on itself, slowing the fuel flow rate.

[Wayne 962]

Have you checked the ignition system and the timing? What may be a fuel system problem may actually be an ignition problem!

Check the total advance, and see if the distributor is advancing the timing correctly...

-Wayne

[Peter Voullaire]

WAYNE TIMING IS PERFECT BEEN DOWN THAT ROAD CHEERS PETE

Originally posted by Wayne at Pelican Parts:
Have you checked the ignition system and the timing? What may be a fuel system problem may actually be an ignition problem!

Check the total advance, and see if the distributor is advancing the timing correctly...

-Wayne

[Peter Voullaire]

Ian, Robert and Wayne.

Thank you for your suggestions. The fuel line sucking in and the fuel accumulator ideas are areas that I have not checked, and will be as soon as I get some spare time.

I look forward to talking with you bin the future.

Cheers Pete V